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In this study, heated silicon oil with added carbon and starch powders was used as dielectric liquid, instead of common hydro-carbon based dielectrics, to obtain better hole surface quality with rotating brass tube electrode in electric discharge machining (EDM). The electro-rheometer tests were conducted to find out the suitable temperature and powder concentration values of the electro-rheological (ER) dielectric under the electric field. Higher workpiece material removal rates (MRR) was obtained in carbon powder added dielectrics than the starch powder added ones for rotating and non-rotating electrodes. The optical microscope observations of the machined hole surfaces indicated that the carbon powder added dielectrics reduced the diameter and depth of the discharge craters, thereby resulting in uniformly distributed and round top peaked surface topography. The starch powder addition to the carbon mixed dielectric further improved the surface quality for both rotating and non-rotating electrodes cases at 30˚C and 75˚C dielectric temperatures.

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In this study, the mechanical and micro-structural properties of injection-molded steatites were investigated experimentally. Initially, steatite powders and binders of polyethylene glycol (PEG), polypropylene (PP), and stearic aside (SA) were mixed to prepare the feedstock. The mixing powders were granulated using the extruder. The short granules in cylindrical shapes were used as the feedstock in the injection-molding operations. Solvent-and thermal-debinding processes were applied to the green samples after the molding. The samples were sintered at 1300°C for 4 h, and a theoretical density of 98-99% was achieved. Threepoint bending and tensile tests were performed on the samples which were sintered at 1200-1300°C. The maximum three-point bending and tensile strength values were found as 154 and 47 MPa, respectively. The morphology of fractured surface was done by scanning electron microscopy whereas porosity investigations were carried out using the same microscopy. Grain growth and structure on the specimens were also investigated using transmission electron microscopy.

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This experimental study aims to reveal the effect of the drill flute number on the thrust force, tool wear, tool life, chip morphology, surface hardness and microstructure in the drilling of a cast AZ91 magnesium alloy. The results showed that the cutting flute number and cutting parameters have an important effect on thrust force, tool life, wear, chip morphology, microstructure, and drilled hole hardness. When the 2-flute drill was used, less thrust force was generated during the drilling. On the other hand, less tool wear occurred with the 3-flute drill. In scanning electron microscopy (SEM) microstructural analyses, grain refinement was observed in the microstructure of the borehole surface although grain growth was also observed due to a rise in temperature. In addition, the microhardness of the borehole surface decreased as the number of holes increased, and the 2-flute drill bit provided holes with higher stiffness than the 3-flute drill bit.

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